The present invention relates to a device for reducing the pressure of a compressor during idling and shut-down.
In the induction manifold of such a device, there is an induction control valve that controls its cross-sectional area. This is bypassed by a bypass channel, the output of which runs through a pressure accumulator to a user. An adjusting device operated from the pressure in the pressure accumulator is provided for the induction control valve, and a return line that can be shut off by a relief valve is fed back to the induction side from the pressure accumulator. The device for reducing the pressure is incorporated in the return line.
As is known, one possibility for controlling the output from compressors and the like, for both piston-type compressors with reciprocating pistons as well as for rotary-type compressors, in particular screw-type compressors, is to vary the open cross-section of the induction manifold and thereby throttle the quantity of medium that is drawn in, either more or less. When this is done, it is not desirable to close off the induction line completely when the compressor is idling since then there will be a relatively large under-pressure in the vicinity of the compressor. This is a disadvantage, in particular, in the case of rotary and, above all else, in the case of screw-type compressors, because when this is done lubrication and cooling of the compressors is interrupted.
It is already known that, in order to avoid this problem, the induction control valve can be bypassed by a bypass channel so that when the compressor is idling there is always a specific minimal output that helps prevent harmful under-pressure in the compressor, but which ensures adequate cooling and lubrication for the compressor.
The quantity of medium that is delivered when idling, even though small, must be fed back to the induction side of the compressor, which can be done in the case of air that is blown off to the atmosphere. It is known that in order to do this, a return line that can be shut off by means of a relief valve can be run back from the pressure accumulator to the induction side and incorporated in a device for reducing pressure.
In known embodiments, the device that is used to reduce pressure consists of a nozzle with a fixed unobstructed cross-section that is of such dimensions that in normal idling operation the pressure that is required to ensure the operation is maintained within the pressure accumulator. For this reason, this reducer nozzle is frequently of relatively small dimensions. The reduction of pressure that is achieved from full operating pressure starting from idling pressure proceeds very slowly. In the same way, the air venting time when the compressor is shut down is correspondingly long. It is determined by the size of the fixed nozzle and the size of the pressure accumulator, as well as by existing operating pressure. The nozzle can be partially obstructed very easily by impurities that are carried in with the medium that is being delivered, for this reduces the unobstructed cross-section and the time required to reduce pressure is made even longer. The result of this is that the medium pressure within the container rises despite the fact that the system is idling. This causes increased energy consumption to drive the system because during this time the compressor operates at an excessively high pressure that must subsequently be reduced.
It is an object of the present invention to improve pressure reduction in compressors in a simple manner so that the desired pressure is achieved both during idling and when the compressor is shut down, this being done as quickly as possible and in a manner that is appropriate for the particular operating conditions.